One such display matrix is known from document EP-0 109 328. The motor comprises a rotor constituted by a small magnet having two poles oriented radially relative to the axis of rotation, and a stator formed by a circuit that is magnetizable by pulses, and that is made of a material having good remanence, and that presents two poles which are diametrically opposite about the axis of the rotor, the rotor including, in the vicinity of each of its poles, an indexing element that is not aligned with the poles of the stator and that is designed to destabilize the position of the rotor at the moment that a pulse occurs. In motors of that type, when the stator receives a pulse of opposite polarity to the preceding pulse, the rotor turns through half a turn, and when the rotor receives two successive same-direction pulses, the second pulse has no effect.
When the disk includes light-blocking sectors alternating with light-transmitting identical sectors, it is connected to the shaft of the motor via a gear unit. Light is masked when the motor receives a pulse in a given direction and light is transmitted when the pulse is in the opposite direction.
Thus, with a masking disk that corresponds to two states, even without actually detecting the relative angular position of the masking disk relative to the fibers, there is never any ambiguity about the state of the mask. Only mechanical blockage preventing the disk from rotating can give rise to non-conformity between the required state and the real state of the mask.
However, as soon as it is desired to use a masking disk that generates more than two states, e.g. to generate different colors or different intensities of light, then it is necessary to make sure that after a given display instruction, the disks actually take up the requested angular positions relative to the optical fibers associated with each of them.
This requirement is particularly necessary in road safety applications where the safety aspect of the display is important and where it is necessary at all times to be able to rely on the quality of the displayed message.